Electrical transmission range shift system

ABSTRACT

A vehicle transmission assembly includes a main gear box and an auxiliary or range gear box. An electrical actuation device for effecting changes in the range gear box preferably includes a solenoid actuator associated with each of the range gear members. A switch, which is preferably provided on the shift lever handle, allows the driver of the vehicle to indicate a desire to make a change in the range gear box. The solenoid actuators are responsive to the electrical switch to effect the range shift. The electrical components replace pneumatic components and associated fittings and airlines used with some prior systems. A further feature of this invention is to include a synchronizer protection circuit that disables the solenoid actuators unless prescribed transmission conditions are met.

This is a continuation of co-pending application Ser. No. 08/997,716filed on Dec. 23, 1997

BACKGROUND OF THE INVENTION

This invention generally relates a system including electrical actuatorsfor changing gears within a vehicle transmission range gear box.

Heavy duty vehicle transmissions typically provide the ability to engagea large number of gear ratios for driving the vehicle. In manyinstances, a main transmission gear box houses a number of gear membersthat are selectively engaged to choose a particular gear ratio. Anauxiliary or range gear box is often also provided to increase thenumber of available gear ratios. The range gear box typically includesone or more range gear members that are selectively engaged to operatethe transmission in one of several ranges. A first range is typicallyassociated with a number of lower gears such as a first gear throughfifth gear, for example. When the range box is shifted into high range,then the same gears in the main gearbox that were used for first throughfifth gear are now used for sixth through tenth gear, for example.

Pneumatic shift actuators generally have been used to effect a change ofgears in the range gear box. Currently available pneumatic componentsshifting actuators include several shortcomings and drawbacks. A numberof the pneumatic components associated with such systems are prone tocontamination and are susceptible to developing air leaks. Suchcontamination or air leaks render the system inoperative or place it ina condition of poor performance, which requires repair or replacement.

Further, pneumatic components can be too slow under some circumstances.For example, when shifting into the high range, under some circumstancesit is possible for the driver to complete the shift in the main gear boxand begin to accelerate the vehicle before the range gear is fullyengaged. This sequence of events is known in the art as "beating therange shift" and introduces the possibility for undesirable wear ordamage to the transmission components.

This invention recognizes the problems and shortcomings associated withconventional transmission systems and provides an improved system. Thisinvention provides a transmission control system that eliminates theneed for some of the conventional components, which are subject tofailure as discussed above, and utilizes an efficient system that isreadily adapted to most heavy duty vehicle transmissions.

SUMMARY OF THE INVENTION

In general terms, this invention includes electrical actuators foreffecting a gear change within the transmission range box. In thepreferred embodiment, electrically powered solenoid actuators areutilized in place of selected pneumatic components and their associatedair lines and fittings. The invention includes a shift switch, which canbe conveniently located on the transmission shift lever, that enablesthe driver of the vehicle to select when a change in the range gear boxis desired.

A transmission control device designed according to this invention hasseveral basic components. A main gear box has a plurality of gears thatare selectively engaged to achieve a desired gear ratio between atransmission input shaft and the range gear box input shaft. A rangegear box has a range input shaft that is coupled to the transmissionmain gear box output shaft and an output shaft that drives the wheels ofthe vehicle. The range gear box includes selectively engagable rangegears. A shift lever is placed within the vehicle and moveable by adriver into a variety of positions that correspond to a desired changein the gear ratio of the main gear box. A range switch, which can bemounted on the shift lever, is operable by the driver of the vehicle toindicate a desired engagement of one of the range gears. An electricalactuation device within the range gear box is responsive to the rangeswitch to effect the desired engagement of the range gears.

In a further enhancement of this invention, a control circuit isincluded that protects the components of the range gear box by disablingthe electrical actuation device unless certain conditions are met. Theelectrical actuation device will only be energized when the transmissionis in a neutral state and when it is feasible to effect the change inthe range gear box.

The various features and advantages of this invention will becomeapparent to those skilled in the art from the following detaileddescription of the currently preferred embodiment. The drawings thataccompany the detailed description can be described as follows:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a transmission system.

FIG. 2 is a schematic illustration of an electrical actuation systemdesigned according to this invention.

FIG. 3 is a schematic illustration of a modified version of the systemshown in FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 schematically illustrates a transmission assembly 20 for use in aheavy duty vehicle, for example. An engine 22 has an output shaft 24that is selectively coupled through a master clutch 26 to an input shaft28 of a transmission main gear box 30. The transmission main gear box 30is any conventional transmission gear box. A shift lever 32 allows anoperator or driver of the vehicle to selectively cause engagementbetween gear members within the main gearbox 30. In the currentlypreferred embodiment, the shift lever 32 is a manual stick shift lever.It should be noted, however, that a shift arrangement where a drivermoves a shift lever to generate signals indicative of a desired gearchange could also be used.

An output shaft 36 from the transmission main gear box 30 is input to arange gear box 38. The range gear box 38 provides the ability to operatethe vehicle transmission in a high or low range, for example. The rangebox 38 preferably has a high range gear member and a low range gearmember that are selectively engaged depending on the desired gear ratio.The output shaft 40 from the range gear box 38 is used to drive thewheels of the vehicle.

This invention includes an electrical actuation device that effects thegear changes within the range gear box 38. The shift lever 32 preferablyincludes a range switch 42 that is supported on the handle portion 44 ofthe shift lever 32. The range switch 42 allows the driver of the vehicleto indicate when a range shift is desired. The range switch 42preferably is configured so that the driver can specify whether a shiftinto the high range or the low range is desired.

FIG. 2 is a schematic diagram 50 of the currently preferred embodimentof this invention. The range shift switch 42 provides a signal to alatching relay having an energizing coil 52 and a responsive switchportion 54. As indicated in FIG. 2, the driver can selectively move therange shift switch 42 into a position indicating a desire to move therange gear box into the high or low range. The switch assembly 42preferably is located within the shift lever handle 44. The portion ofFIG. 2 outlined at 56 represents a portion of the shift lever wiringharness that is already present within most heavy duty vehicletransmission systems. A plurality of connector units 58, 60 and 62provide a convenient and useful interface between the shift knob wiringharness 45 and a transmission wiring harness outlined at 64. Theconnectors 58, 60 and 62 can be any commercially available electricalconnectors that provide the abilities for switching and selectiveenergization as will be described in more detail below.

A power source, schematically illustrated as a battery connector 66, isassociated with the typical vehicle wiring harness and provideselectrical power to the various components of a system designedaccording to this invention. In the illustrated embodiment, A is thepositive terminal and B goes to the negative terminal. The transmissionwiring harness 64 includes a wiring arrangement 68 that, when used inconnection with the range shift switch arrangement, allows selectiveenergization of a first solenoid 70 or a second solenoid 72.

The first solenoid 70 preferably is associated with the high range gearmember in the range gear box 38. The second solenoid 72 preferably isassociated with the low range gear member. A significant advantage isprovided by utilizing the solenoids 70 and 72. Each of the solenoidsreplace components that were purely pneumatic in prior art systems. Thesolenoids provide the movement or actuation within the range gear box 38that will cause proper engagement of the selected range gear member.

The solenoids are wired through the connector portion 60 so that thesolenoid 72 is activated or energized when the range shift switch 42 isin the position illustrated in FIG. 2, for example. This can beaccomplished by a simple movement of the driver's thumb, for example.

A neutral switch 74 is included for indicating when the main gear box 30is in neutral. The neutral switch 74 preferably is closed when the maingear box 30 is placed in neutral. The neutral switch 74 can beresponsive, for example, to neutral within the main gear box 30. Thewiring arrangement 68 and the operative function of the connector 60insures that the solenoids 70 and 72 will only be energized when theneutral switch 74 is closed and the main gear box 30 is in a neutralcondition. This insures that there is no attempt to engage the rangegear members unless the transmission is in neutral.

The components schematically illustrated in FIG. 2 preferably replacethe slave valve, pneumatic shift knob, and all related air lines andfittings that would otherwise be required in prior art systems.Therefore, this invention eliminates the use of some pneumaticcomponents that can be undesirably slow in response to a driver's desireto effect a range shift. Moreover, pneumatic components introduce thepossibility for defects and failures that do not exist when usingelectrical components as described in this specification. The electricshift knob, electrically controlled solenoids 70 and 72, the neutralswitch 74 and the wiring harness 64 further provide the advantage of acompact, easy to assemble arrangement that is readily adapted to mosttransmissions. The range shift switch 42 allows the driver of thevehicle to pre-select a desired range shift prior to shifting thetransmission to neutral. The actual range shift will occur only when themain gear box 30 is placed in neutral and neutral switch 74 closes. Thisprovides the significant advantage of replacing complex mechanicalinterlock systems that are otherwise required with current pneumaticrange shift actuators. Although not specifically illustrated, thearrangement of FIG. 2 could be modified to include an electricallycontrolled splitter shift system by adding another solenoid andpreferably an additional electric switch on the shift knob 34.

FIG. 3 illustrates an enhancement of the embodiment of FIG. 2. A rangeprotect switch 82 is provided. The range protect switch 82 indicateswhen it is safe for, engaging one of the gear members within the rangebox 38. The circuitry 68' within the wiring harness 64 is slightlymodified compared to that of FIG. 2. A diode 84 is added to interconnectthe grounded terminals of the neutral switch 74 and the range protectswitch 82. This arrangement, in combination with the connections throughthe connector 60 ensures that the solenoids 70 and 72 will only beactivated when the transmission is in a neutral condition and the rangeprotect switch 82 indicates that a range shift is possible.

Power to the solenoids 70 and 72 is supplied via the wires in the shiftknob wiring harness 45, shift lever wiring harness 56, and transmissionwiring harness 64. The range protect switch 82 is added to protect thelow range, the high range, or both low and high range solenoids. Nopower is supplied to the protected circuit when the main gear box 30 isin gear and the range box 38 is not because power is only available whenthe range protect switch 82 is closed (i.e., when the range gear box 38is in gear) and the neutral switch 74 is closed (i.e., when the maingear box 30 is in neutral).

The range protect switch 82 is open whenever the range box 38 is not ingear. For example, when the range box 38 is still shifting, the rangeprotect switch 82 is opened and power to the solenoid is providedthrough the neutral switch 74. If the main box lever shift is completed,the neutral switch 74 opens and if the range shift is not complete thenpower is cut to the solenoid that is responsible for effecting the rangeshift. In this manner, the synchronizer is protected.

In the event that the range box has not completed its shift, the maingear box 30 must be returned to neutral so that neutral switch 74 canclose and the range shift can be completed. When the range shift iscomplete, the switch 82 is closed. The solenoid remains powered andholds the range box in the selected gear range.

The embodiment illustrated in FIG. 3 is arranged to protect the high andlow range synchronizer. The embodiment of FIG. 3A illustrates how theembodiment of FIG. 3 can be modified to protect only the high rangesynchronizer. The embodiment of FIG. 3b illustrates how the embodimentof FIG. 3 can be modified to protect only the low range syncronizer.

The range protect switch 82 provides the advantage of preventingsynchronizer failures by disabling the appropriate solenoid(s). When thesolenoids are disabled they cannot cause engagement of the selectedrange gear member. Therefore, high range synchronizer damage isprevented in the event that the operator attempts to accelerate thevehicle before the shift in the range box 38 is complete. Thisrepresents a significant difference compared to prior are systems wherea pneumatic actuator continues to engage the synchronizer materialdespite the conditions of the main gear box 30 being engaged and adriver attempting to accelerate the vehicle. The synchronizer protectioncircuitry of this invention is also effective for protecting thesynchronizers associated with engaging a low range gear, which mayoccur, for example, during a down-hill coast when the driver has theaccelerator pedal released after having engaged the gears within themain gear box 30 before the synchronizers in the range gear box havecompleted the range shift.

Accordingly, this invention accounts for a synchronizer failure modethat is known to exist with current systems. Sometimes a discrepancyexists between the time required to complete range synchronization andthe ability of a driver to shift the transmission main gear box fasterthan the automated components. This known failure mode is often referredto as a "beat range shift" and occurs most often when an operator of thevehicle fails to properly pre-select a range shift according to approveddriving procedures or when some of the range shift system components donot perform at full capacity.

The combination of the neutral switch 74 and the range protect switch 82acts as a range detector that indicates when the transmission is in acondition conducive to the selected range gear being engaged.

The preceding description is intended to explain this invention by wayof example. Variations and modifications to the embodiments describedabove may become apparent to those skilled in the art. Such changes oradditions, however, do not necessarily depart from the purview andspirit of this invention. The legal scope of protection given to thisinvention can only be determined by studying the following claims.

We claim:
 1. A vehicle transmission assembly, comprising:a main gear boxhaving a plurality of gears that are selectively engaged to effect adesired transmission gear ratio; a range gear box coupled to saidtransmission and including selectively engagable range gears; a shiftlever that is movable to indicate a desired change in the gear ratio ofsaid main gear box; a range switch that is operable by an operator ofthe vehicle to indicate a desired engagement of one of said range gears;and an electrical actuation device within said range gear box that isresponsive to said range switch to effect selective engagement of saidrange gears.
 2. The assembly of claim 1, wherein said electricalactuation device includes a solenoid.
 3. The assembly of claim 1,wherein said range gears include a high range gear member and a lowrange gear member and said electrical actuation device includes a highrange solenoid that effects engagement of said high range gear memberand a low range solenoid that effects engagement of said low range gearmember.
 4. The assembly of claim 1, wherein said shift lever is a manualshift lever that is coupled to portions of said main gear box gears tomanually effect changes in the gear ratio.
 5. The assembly of claim 1,wherein said shift lever is coupled to a signal generator and said leveris moveable to generate electrical signals that are indicative of adesired gear change and said main gear box includes an actuationarrangement that effects the desired change responsive to saidelectrical signals.
 6. The assembly of claim 1, wherein said electricalactuation device includes a solenoid actuator associated with each ofsaid range gears.
 7. The assembly of claim 6, wherein said range switchis operative to cause a selected one of said solenoids to be energizedto thereby effect a desired engagement of said range gears.
 8. Theassembly of claim 7, wherein said range gears include a high range gearmember and a low range gear member and said electrical actuation deviceincludes a high range solenoid that effects engagement of said highrange gear member responsive to appropriate actuation of said rangeshift switch and a low range solenoid that effects engagement of saidlow range gear member responsive to appropriate actuation of said rangeshift switch.
 9. The assembly of claim 1, further comprising a neutralindicator associated with said transmission that indicates when saidtransmission is in a neutral condition and wherein said electricalactuation device is only responsive to said range shift switch when saidneutral indicator indicates that said transmission is in said neutralcondition.
 10. The assembly of claim 1, further comprising a rangedetector that indicates when said transmission is in a conditionconducive to said range gears being engaged and wherein said electricalactuation device is only responsive to said range shift switch when saidrange detector indicates that said conducive condition exists.
 11. Theassembly of claim 10, wherein said range detector is effective todisable said electrical actuation device whenever said conducivecondition does not exist.
 12. The assembly of claim 10, wherein saidconducive condition includes said transmission main gear box being inneutral.
 13. A method of effecting gear changes in a vehicletransmission assembly including a range gear box having a plurality ofrange gear members and an electrical actuator associated with the rangegear members comprising the steps of:(A) indicating that a selected oneof the range gear members should be engaged; (B) determining whetherengagement of the selected range gear member is possible; and (C)activating the electrical actuator when engagement of the selected rangegear member is possible until said selected range gear member is engagedor such engagement becomes no longer possible.
 14. The method of claim13, wherein step (A) is performed by manually manipulating a rangeselection switch.
 15. The method of claim 13, wherein step (B) isperformed by determining whether the transmission is in a neutralcondition and wherein step (C) is performed only when the transmissionis in a neutral condition.
 16. The method of claim 13, wherein step (B)is performed by determining whether the transmission is in a neutralcondition and determining whether a beat shift condition exists thatincludes gear members within a main gear box being engaged and thevehicle being accelerated and wherein step (C) is performed only whenthe transmission is in a neutral condition and the beat shift conditiondoes not exist.
 17. The method of claim 16, wherein step (C) isperformed by the substep of deactivating the electrical actuatorwhenever the beat shift condition exists prior to the selected rangegear member being fully engaged.
 18. A system for controlling engagementof gear members within a vehicle transmission range box, comprising:arange box assembly including at least one selectively engagable gearmember; a selection switch that is manually operable by a driver of thevehicle to indicate when engagement of the gear member is desired; andan electrically powered actuator supported within said range boxassembly and operatively associated with said gear member to selectivelyengage said gear member responsive to operation of said switch.
 19. Thesystem of claim 18, further comprising a detector that detects whetherthe vehicle transmission is in a condition conducive to said range gearmember being engaged and wherein said detector is operative todeactivate said electrically powered actuator whenever the transmissionis not in said conducive condition.
 20. The system of claim 18, whereinsaid range box assembly includes a high range gear member and a highrange electrically powered actuator associated with said high range gearmember, a low range gear member and a low range electrically poweredactuator associated with said low range gear member, wherein saidselection switch is operable to indicate which of said electricallypowered actuators is to be activated and further comprising a protectordevice that is operative to disable said actuators whenever thetransmission is in a predetermined condition.